Helical coils using mothball filler



Nov. 19, 1968 E. HIMSTEDT 3,411,195

HELICAL COILS USING MOTHBALL FILLER Filed Feb. 4, 1966 INVENTOR. EPIC/J Hms 7507' JOHN 5 M: 14 44- nrrae/va s United States Patent 3,411,195 HELICAL CQILS USING MOTHBALL FILLER Erich Himstedt, Monrovia, Calif., assignor to American Standard Inc., a corporation of Delaware Filed Feb. 4, 1966, Ser. No. 525,237 2 Claims. (Cl. 29-157) ABSTRACT OF THE DISCLOSURE This invention relates to a method of forming thin walled Bourdon coils having small cross-sectioned passages therein. The method comprises filling a partially flattened tube with liquid filler, maintaining the tube in an upright condition while allowing the tube to cool and the filler to harden from bottom to top so as to cause superjacent liquid to drain into void areas, further flattening the tube to reduce voids, winding the tube into a coil shape, and removing the filler from the coil.

In the drawings:

FIG. 1 is an elevational view of a Bourdon coil formed by the method of this invention.

FIG. 2 is a bottom plan view of the FIG. 1 coil.

FIGS. 3 and 4 are sectional views taken through a tube before and after flattening during practice of the method of this invention.

FIG. 5 is a schematic view showing the step of flattening a tube during practice of the invention.

FIG. 6 is a view schematically illustrating an apparatus useful in the practice of this invention.

FIG. 7 is a schematic view showing the step of further flattening the FIG. 5 tube.

FIG. 8 is a plan view of an apparatus useful in the coiling of a Bourdon tube in the practice of this invention.

FIG. 9 is an end view of the FIG. 8 apparatus.

Referring more particularly to the drawing, there is shown in FIG. 1 a helical Bourdon coil useful for example in fluid pressure gauges to measure fluid pressures ranging for example from 0 to 100 p.s.i. The coil comprises a circular tubular portion 10 which may be soldered or otherwise secured wi-thin a gauge housing (not shown) to mount the coil. Extending laterally from mounting portion 10 is a cylindrical portion 12 which merges with the first convolution of a helical coil section designated by numeral 14. It will be noted that the walls of the coil section are flattened, as at 16 and 18. The upper convolution of the coil is turned radially inward as at 20, after which the open end 19 is closed, as by solder or the like. A pointer (not shown) may be attached directly to portion of the coil so that introduction of pressure fluid through mounting portion 10 causes helical section 14 to unwind about its axis 21, thereby producing a pointer rotation which is a measure of the pressure sensed by the coil.

The Bourdon coil may be constructed of Inconel X tubing having a diameter of .080 inch and :a wall thickness of about .0027 inch. The coil may have a total length on the order of 9 inches and a coil diameter radius D of about .35 inch. The spacing between wall surfaces 16 and 18 may be on the order of .006 inch. Such a coil can be used to sense pressures in a range from 0 to 100 p.s.i. The coil is of course heat treated to act as a spring for resisting the fluid pressure and automatically winding itself back toward its initial condition in response to lowering internal fluid pressures.

During the formation of a coil having a diameter of .35 inch and a tube wall thickness of .0027 inch there is danger that the walls will buckle inwardly into a dogbone configuration unless tubing is filled with a solid material prior to the coiling operation. The dogbone configuration has been found objectionable for low pressure coils in the 0 to p.s.i. in that it gives nonlinear movement per unit pressure change, and unsatisfactory fatigue life. Therefore, it is believed that the use of a filler material in the formation of low pressure coils is a necessity.

The coils of FIGS. 1 and 2 may be formed from a straight length of cylindrical tubing by the apparatus shown in FIGS. 5 through 9. The procedure involves first flattening the tube along the major portion of its length by the FIG. 5 apparatus. A number of the flattened tubes are then positioned upright in a mass of liquid filler material within container 26 of the FIG. 6 apparatus, thus allowing the liquid to fill the tube interior spaces. Thereafter, the liquid is chilled and thus hardened by flowing cold water through heat exchanger 28. Any voids in the hardened filler are removed by further flattening the tube in the FIG. 7 apparatus. The flattened filled tube may thereafter be formed into a helix on the FIG. 8 apparatus. Removal of the filler may be effected by heating the helix, as by immersing same in a body of hot water.

For best re-inforcement of the coil walls during coil formation the filler material should completely fill the tube with no voids therein. Under the present invention such voids are prevented by filling the tube (FIG. 6), and then pressing or flattening the tube (as shown in FIG. 7) before the coiling operation. In this way any voids which may occur during the filling operation are removed before the coiling step.

Working with thin wall tubing on the order of .0027 inch there is a possibility that a pre-filled tube will rupture during any drastic flattening operation. For example, as shown in FIGS. 3 and 4, a single step flattening of a circular tube would effect a reduction in the internal tubing volume on the order of five times or more; if a thinwalled circular tube were filled with a filler material and then flattened to the FIG. 4 configuration there would be danger that the tube would rupture even though the ends of the tube are open While the tube is being flattened. To avoid this happening, in this invention the cylindrical tube is partially flattened before being filled with the filler material. The subsequent final flattening of the tube therefore does not involve such a radical change in the tube internal volume as would rupture the thin tube walls.

In practicing the invention a straight length of circular tubing 25 may be passed between rollers 22 and 24 as shown in FIG. 5 to effect a first tube flattening operation. The tube is preferably flattened only in those portions which go to form the coil section 14. Thus, tube portions 10, 12, and 20 are not flattened. Therefore, roller 24 may be mounted on a retractable structure (not shown) to permit its retraction away from the tube after a desired length of the tube has been flattened.

Flattened tubes may be filled with a filler material by the apparatus schematically shown in FIG. 6. As there shown, the apparatus comprises a cylindrical upright container 26 having a bottom wall which underlies a spiral heat exchange coil 28. The outer convolution of coil 28 connects with a water line 30 which communicates with two water valves 32 and 34, said valves individually controlling the flow of hot and cold water from sources H and C. It will be understood that by opening valve 32 and closing valve 34 hot water at a temperature for example of F. may be passed through heat exchange coil 28. Similarly, by closing valve 32 and opening valve 34, cold water at a temperature for example of 50 F. may be passed through heat exchange coil 28.

Container 26 may be filled to a predetermined level with a suitable liquid filler material, preferably p-dichlorobenzene. This material has a melting point of about 128 F. Therefore, the material can be kept in a liquid condition in container 26 by the flow of hot Water from source H through heat exchange coil 28. As shown in FIG. 6, container 26 accommodates a removable cylindrical receptable 30 having a foraminous bottom wall 32, of fine mesh screening or perforated metal. The upper edge of receptacle 30 may have a flange 34 which can rest on the upper edge of container 26 to limit insertion of receptacle 30 into container 26 to a position wherein foraminous bottom wall 32 is closely adjacent the bottom wall of container 26.

Receptacle 30 may be packed with a large number of pre-flattened tubes 25, said tubes being arranged closely adjacent one another in upright positions. As receptacle 30 is lowered into container 26 the liquid filler material in container 26 fills the tubes 25. After the filling operation valve 32 may be closed and valve 34 opened. In this way heat exchanger 28 gradually cools the walls of the container 26 and the filler material in the tubes. The filler thus hardens to a solid state. The cooling action will proceed from the lower portions of the tubes upwardly so that contraction of the filler material during the liquidsolid transition will create voids which will immediately be filled by superjacent liquid draining into the void spaces. Thus, the filled and cooled tubes will have a lessened number of voids therein.

After the cooling operation receptacle 30 may be removed by a pull on the cross rod 36. Thereafter, the filled tubes may be removed from receptacle 311 and further flattened in the apparatus shown schematically in FIG. 7. As shown, the apparatus comprises a pair of rollers 33 and 40, one of said rollers being a powered roller to drive the tubing between the rollers and effect a final flattening of the tube. During this final flattening operation the filler material is densified and more tightly packed into the tube, thus removing most of the voids which may have occurred during the filling or cooling steps.

The flattened tube may be coiled by the apparatus shown in FIGS. 8 and 9. As there shown, the apparatus comprises a cylindrical mandrel 42 having a slot 44 for accommodating the cylindrical end portion 20 of the flattened tube. The back wall of the slot may be angled in accordance with the desired pitch of the coil helix turns. Cooperating with mandrel 42 is an idler roller 46 spaced from roller 42 by the desired radial thickness of the coil convolution. With tube 25 held in its FIG. 8 position, mandrel 4-2 may be rotated around its central axis to wind the fiat portion of the tubing around the mandrel. Roller 46 serves as an ironing means to maintain the tubing against the mandrel surface during the coiling operation.

p-Dichlorobenzene is a particularly desirable filler material during the coiling operation because it possesses a satisfactory compromise between rigidity and softness. Thus, during the winding period it re-inforces the tube with a suflicient rigidity ot prevent dogbonning or wrinkling. At the same time it is sufliciently soft as to have some plastic flow without rupturing the thin tube walls.

After the coiling operation, the dichlorobenzene filler material may be removed from the tube by submerging the coil in a hot water bath. p-Dichlorobenzene is somewhat soluble in water and has a melting point of about 128 F. Therefore, the filler undergoes both a melting and dissolving process when the coil is submerged in hot water, such that substantially all of the material is removed from the finished coil. If desired, hot water can be flushed through the coil to further remove the filler material.

Following the filler-removing operation the coil is preferably dried at an elevated temperature, as for example, 250 F., after which the coil can be heat treated to provide the desired spring in the coil.

It will be understood that the invention can be practiced with some variation as comprehended by the amended claims.

What is claimed:

1. The method of forming a Bourdon coil comprising the steps of partially flattening a straight circular crosssectioned tube; filling the tube with a liquid filler material by positioning the tube in an upright condition within a mass of the material; cooling the tube to harden the filler material, said cooling step being carried out by cooling the lower portion of the tube while it is in its upright condition so that liquid filler material drains into voids created by the hardening process; further flattening the tube to eliminate any voids in the filler material caused by the hardening step; winding the filled and flattened tube into a multi-convolution coil; and removing the filler material from the coil.

2. The method of claim 1 wherein the filler material is p-dichlorobenzene.

References Cited UNITED STATES PATENTS 1,827,766 10/1931 Rosenburgh.

2,841,866 7/1958 Schilling 29-423 3,251,126 5/1966 Himstedt 29-423 3,343,250 9/1967 Berto et al 29423 JOHN F. CAMPBELL, Primary Examiner.

PAUL M. COTTEN, Assistant Examiner. 

